The idea of harmonisation is extremely worthwile, even if it takes 30 years to fit out all mainlines. Such interoperability issues is what keeps rail freight from achieving what it an on the most ideal distances -- when 600-1000 km crosses borders...

I should also underline that ERTMS Level 1 (in which signals are given only by fixed magnets in the middle of the track, the "Eurobalises") is not problematic, and I think having it everywere would be a plus even if some of the current national signalling systems allow a higher train frequency.

For ERRTMS Level 2, I think the problem is clearly the system chosen. (Though I imagine that getting a conventional cable and lineside signal based, high-speed-capable signalling system would face the difficulty of choice -- e.g. the fight between something based on the French TVM430 or the German LZB.)

To put it simply: it is but a minute nuisance if you lose signal in the middle of a phone call and the call breaks off, in say every 20th call. But when that happens for a continuous signalling system, the train will have to stop. So normal 3G wireless is just not stable enough for this purpose. You can try to get through signal holes with software, but the HSL Zuid experience seems to show that may not be a universal patch.

Maybe ERTMS Level 2 will one day master these problems fully, I don't know -- but when just in Italy, two years of experience on two lines running on ERTMS Level 2 only is not enough, I'm not optimistic.